Environment

Weakening Current

The strength of the Florida Current, which marks the beginning of the Gulf Stream, has weakened in force to the lowest level of the past 110 years, according to new research.

The current flows between Florida and Cuba before becoming the Gulf Stream near the Bahamas.

While precise measurements of the current go back to only the early 1980s, scientists say they were able to determine its past strength by how it affected coastal sea levels in the region.

The study confirms earlier findings that show the Atlantic Meridional Overturning Circulation is slowing down due to climate change. That complex of currents wields a key warming influence across the Atlantic to much of northern Europe.

Global Warming

Climate Change is Pushing Giant Ocean Currents Poleward

The world’s major wind-driven ocean currents are moving toward the poles at a rate of about a mile every two years, potentially depriving important coastal fishing waters of important nutrients and raising the risk of sea level rise, extreme storms and heatwaves for some adjacent land areas.

The shift was identified in a new study by researchers with the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, Germany, and published Feb. 25 in the journal Geophysical Research Letters.

The poleward shift is bad news for the East Coast of the U.S., because it makes sea level rise even worse, the researchers said. At about 40 degrees latitude north and south, where the effects of the shifting currents are most evident, sea level rise is already 8 to 12 inches more than in other regions.

On the West Coast, salmon are being pushed out of traditional fishing waters. In densely populated coastal Asia, the changes could unleash more intense rainstorms, and the shift also makes heat waves more likely in subtropical areas.

Eight major wind-driven ocean currents, known as gyres, circulate around vast areas of ocean: three in the Atlantic, three in the Pacific, and one each in the Indian and Antarctic Oceans. The rotating currents shape the weather and ocean ecosystems in coastal regions, where parts of the currents have regional names, like the Gulf Stream along the East Coast of the U.S.

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Global Warming

Weaker Ocean Currents

A new study has found evidence that the ocean circulation in the North Atlantic has become the weakest of the past 1,500 years, mainly as a result of a warming climate.

Many climate models predict a weakening, or even a collapse, of this branch of the ocean circulation under global warming — partly due to a surge of fresh water from the melting of the Greenland ice sheet.

Researchers from the University of Hong Kong write in the journal Geophysical Research Letters that the Atlantic Meridional Overturning Circulation has far-reaching impacts on the climate from North America to Europe, and can influence the monsoon rainfall in South Asia and Africa.

CO2 Emissions Surge

Global emissions of the most prevalent greenhouse gas, carbon dioxide, rose to a new historic high last year, according to a U.N. report that warns the time for action to avoid disastrous climate change is running out.

It adds that emissions began rising again during 2017 for the first time in four years. Levels of accumulated atmospheric CO2 reached a global average of 405.5 parts per million during 2017, almost 50 percent higher than before the Industrial Revolution.

“The last time the Earth experienced a comparable concentration of CO2 was 3 to 5 million years ago, when the temperature was 2 to 3 degrees Celsius (3.6 to 5.4 F) warmer and sea level was 10 to 20 meters (33 to 66 feet) higher,” said World Meteorological Organization Secretary-General Petteri Taalas.

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Global Warming

Worrisome prediction about climate change coming true

Two years ago, former NASA climate scientist James Hansen and a number of colleagues laid out that possibility that gigantic pulses of fresh water from melting glaciers could upend the circulation of the oceans, leading to a world of fast-rising seas and even superstorms.

Hansen’s theory was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate scientists. But now, a new oceanographic study appears to have confirmed one aspect of this picture, in its early stages, at least.

The new research, based on ocean measurements off the coast of East Antarctica, shows that melting Antarctic glaciers are indeed freshening the ocean around them.

And this, in turn, is blocking a process in which cold and salty ocean water sinks below the sea surface in winter, forming ‘‘the densest water on the Earth,’’ in the words of study lead author Alessandro Silvano, a researcher with the University of Tasmania in Hobart, Australia.

Environment

Climate-Regulating Ocean Current Is the Weakest It’s Been in 1,500 Years

In the Atlantic Ocean, the current known as the Atlantic Meridional Overturning Circulation (AMOC) ferries warm surface waters northward — where the heat is released into the atmosphere — and carries cold water south in the deeper ocean layers, according to the National Oceanic and Atmospheric Administration. Its circulation transports heat around the globe like a conveyor belt, and if its movement were to stop, that heat would not get distributed, and weather havoc could ensue.

But the AMOC has been getting weaker, and cold, freshwater infusions by the runaway melting of glaciers, sea ice and permafrost are to blame, and the AMOC may weaken even further if temperatures on Earth continue to rise and ice reserves continue to melt, scientists reported in the two studies.

A research team estimated that, since the current began to lose strength in the mid-1800s, it has weakened by about 15 to 20 percent.

Prior research has suggested that a feeble AMOC brings more dryness to the Sahel, a region of Africa bordering the Sahara Desert; spurs sea-level rise in U.S. coastal cities; and encourages patterns of increasingly cold winters in Europe and the northeastern U.S.

New Ocean Current Discovered Off the Coast of Madagascar

A previously unknown ocean current was recently discovered “by accident” off the coast of Madagascar, a rare find in the 21st century.

In oceanic terms, the Southwest Madagascar Coastal Current is fairly small: At only 62 miles (100 kilometers) long and 330 yards (300 meters) deep, it transports about 264 million gallons (1.3 gigaliters) of warm, salty water a second, or the equivalent of more than 500 Olympic swimming pools’ worth of water.

But the current’s location, rather than its size, makes it vital in understanding the world’s oceans, the researchers said. The Mozambique Channel feeds the Agulhas Current, one of the strongest currents in the world. The Agulhas Current affects the path of tropical storms and carries heat toward higher latitudes. The Agulhas is the equivalent of the Gulf Stream, but for [the] Southern Hemisphere.

Global Warming

Global Warming Is Slowing Ocean Currents

Climate scientists Michael Mann and Stefan Rahmstorf announced the findings of their new study yesterday, which shows that the rapid melting of the polar ice has slowed down currents in the Atlantic Ocean, particularly since 1970. The scientists say “the slowdown in ocean currents will result in sea level rise in cities like New York and Boston, and temperature changes on both sides of the Atlantic,”.

Mann explains the consequences of the Gulf Stream shutting down and how it would drastically alter the climate in Europe and North America. The last time this happened, about 12,000 years ago, at the end of the last ice age, North America and Europe went back into a mini-ice age, Mann says. Not only would North America and Europe experience colder temperatures, but “If those current systems shut down, then suddenly the North Atlantic [fisheries] would no longer be productive,” says Mann.

Mann says a shutdown of the Gulf Stream might happen a lot sooner than the latest Intergovernmental Panel on Climate Change (IPCC) report predicts. “Our studies suggest we are much closer to that than the current model suggests. A full shutdown … could be decades from now.”